The present invention relates to compositions, and methods of use, which provide improved efficacy in controlling Phytophthora infections in plants. More particularly, the composition is comprised of an amount of phosphate (PO4) and phosphonate (PO3), with application of such composition particularly useful in lowering the occurrences of late blight.
From 1845 to 1846, the Irish Potato Famine occurred, which was one of the most devastating crop failures in the history of the world. The potato famine was caused by the disease late blight which resulted in harvested potatoes quickly decaying, making them unsuitable for consumption. The disease is also known to cause defoliation in infected plants. Late blight is caused by a Phytophthora organism infecting a potato or tomato plant. As can be gathered, the Phytophthora organism, if not controlled, can cause major economic damage to agricultural crops, with the resulting damage causing the loss of millions of dollars in crop revenues. Additionally, there is the possibility of significant reduction of the potato and tomato supply available to consumers.
To control late blight, it has been recommended that the contaminated potatoes and/or tomatoes be buried in deep pits and covered by at least two feet of soil. In Northern Latitudes, the potatoes or tomatoes can be spread on the soil surface and allowed to freeze during the winter. These methods temporarily prevent the spread of the disease, but do not prevent infection and attack by the Phytophthora infestans. The treatment only addresses plants and crops after they have been destroyed. For this reason, it is desired to have a composition or method that can be administered to potato and tomato fields to actively control and prevent the spread of the Phytophthora infestans infestation.
Some species of the Phytophthora genus can be controlled, such as Phytophthora parasitica. In particular, fosetyl-al (ethyl phosphonate) can be administered to plants to control diseases such as root rot caused by Phytophthora parasitica. As such, it is known that many phosphonate (PO3) compositions are highly effective in combating the disease root rot and, in particular, some of the species of the genus Phytophthora. Unfortunately, fosetyl-al and other phosphonates, alone, do not control late blight and similar Phytophthora diseases caused by the species Phytophthora sojae. Thus, it is desired to have a method or composition that readily inhibits infection by and proliferation of Phytophthora infestans. 
Phosphorus is an essential element in plant nutrition because it governs the energy producing reactions, including those that are oxidative and photo phosphorylative. Phosphorous is essential to the production of adenosine diphosphate (ADP) and adenosine triphosphate (ATP). Energy-rich phosphate bonds of ADP and ATP provide the energy for many of the physiological reactions that occur in plants. As such, various forms of phosphorous are absorbed by plants for use as part of the photosynthetic process.
The element phosphorous appears in numerous general forms, including phosphonate (PO3) and phosphate (PO4). The term xe2x80x9cphosphonate,xe2x80x9d sometimes also referred to as xe2x80x9cphosphite,xe2x80x9d means the salts (organic or inorganic) of either phosphonic acid or phosphorous acid. Phosphonic and phosphorous acids have the formula H3PO3 and a molecular weight of 82.00. Their structures from the International Union of Pure and Applied Chemistry are shown below: 
The term xe2x80x9cphosphatexe2x80x9d means the salts (organic or inorganic) of phosphoric acid having the formula H3PO4, molecular weight of 98.00 and having the following structure: 
In the past, various phosphonate compounds have been proposed as useful in fungicidal and fertilizer compositions for application to plants. See, e.g. U.S. Pat. Nos. 4,075,324 and 4,119,724 to Thizy, describing phosphorous acid, its inorganic and organic salts, as a plant fungicide; U.S. Pat. No. 4,139,616 to Dueret, describing fungicidal compositions based on phosphorous acid esters and salts thereof; U.S. Pat. No. 4,542,023 to Lacroix et al., describing organophosphorous derivatives as possessing systemic and contact fungistatic and fungicidal activity; U.S. Pat. Nos. 4,698,334, 4,806,445, and 5,169,646 to Horriere et al., describing fungicidal compositions based on alkyl phosphonates; U.S. Pat. Nos. 4,935,410 and 5,070,083 to Barlet, describing fungicidal aluminum tris-alkyl-phosphonate compositions; and U.S. Pat. No. 5,514,200 to Lovatt, describing formulations of phosphorous-containing acid fertilizer for plants. (The teachings of the proceeding U.S. Patents are hereby incorporated by reference.) The above references, disclosing phosphonate compositions, have been found to be effective for protecting plants and, particularly, grape vines, citrus and fruit trees, and tropical plants against fungal attack.
Note that phosphonate (PO3) alone is typically considered an unacceptable source of phosphorus (P) for plants. It is known that PO3 must be converted to PO4 to be utilized by a plant.
Once assimilated, phosphonates (PO3) have been shown to enhance the plant""s phytoimmune system. The phosphonate induced stimulation of the phytoimmune system is triggered by the induction of ethylene production, followed by a rapid accumulation of phytoalexins at the site of infection. Phytoalexins are antibiotics which result from the interaction between the host plant and a pathogen. The phytoalexins are synthesized by and accumulate in the plant to inhibit the pathogen. The phytoalexins will accumulate at the site of an infection to prevent further spread of the disease, thereby reducing symptomatic expression of the disease.
In the past, phosphates (PO4) were not viewed as a solution to pathological acerbation of fungal infections or infections produced by other genuses. This is because phosphates (PO4) are viewed primarily as a fertilizer with only limited, or even detrimental, phytoimmune properties. For example, U.S. Pat. No. 5,514,200 teaches that phosphate fertilizers inhibit beneficial symbiosis between plant roots and mycorrhizal fungi, and further promote bacterial and fungical growth in the rhizosphere, including the growth of pathogenic fungi and other small soil-borne organisms. (Col. 2, lines 18-28). Phosphates (PO4) have also been considered to be a competitive inhibitor for phosphonate assimilation, thus inhibiting the ability of phosphonates (PO3) to protect against fungus attack. See, Pegg, K. G. and deBoer, R. F., xe2x80x9cProceedings of the Phosphonic (Phosphorous) Acid Work Shop,xe2x80x9d Australiasian Plant Pathology, Vol. 19 (4), pp. 117 and 144, 1990. Yet further, phosphonates (PO3) and phosphates (PO4) were believed to be xe2x80x9cbiological strangers,xe2x80x9d with the presence of phosphonates (PO3) or esters of phosphonates, exerting little or no influence on enzyme reactions involving phosphates. Robertson, H. E. and Boyer, P. D., xe2x80x9cThe Biological Inactivity of Glucose 6xe2x80x94phosphonate (PO3), Inorganic Phosphites and Other Phosphites,xe2x80x9d Archives of Biochemistry and Biophysics, 62 pp. 380-395 (1956).
Accordingly, the requirements for a successful phosphonate-based fungicide depend on the promotion of the phosphonate-induced pathological acerbation of fungical or other genus infections. More particularly, it is desired to have a composition and/or method that prevents Phytophthora infestans infection and destruction of plants.
The present invention relates to compositions and methods for use in preventing infection by and manifestations of the genus Phytophthora and, more particularly, Phytophthora infestans. The composition will be comprised of phosphate (PO4) and phosphonate (PO3) constituents which, when combined, provide for a synergistic effect that results in the substantial protection against infection of plants by Phytophthora, especially Phytophthora infestans. As such, the phosphate and phosphonate constituents can be combined to form a composition, which can be applied to plants, especially tomatoes and potatoes, to prevent infection by Phytophthora infestans and diseases caused by such infection. Application can be achieved by using either a dry mix or an aqueous solution.
The preferred composition for preventing Phytophthora will be comprised of potassium phosphonate and potassium phosphate, as it has been found that these two constituents, when combined, will cause a synergistic effect which results in the substantial prevention of infection by Phytophthora. It is believed, that the rate by which infection is prevented is increased by at least 100% when the two constituents are combined, as compared to the additive effect of the combined salts. The two constituents will be combined in an amount sufficient to prevent infection and manifestation by various disease causing organisms, with the particular amounts combined dependent upon the particular species of plant to be treated, the specific disease causing organism to be treated, and the particular phosphate salt and phosphonate salt that will be combined.
The composition should be applied at least once to the plants to be treated. While one application is sufficient, it is typically preferred to make multiple applications. Essentially, any plant infected by Phytophthora can be treated, with it most preferred to apply the composition to potato and tomato plants. It should also be noted that the composition not only inhibits Phytophthora, but is environmentally safe, inexpensive to use, and has low mammalian toxicity.
Preferably, the composition will contain as an active material an effective amount of at least a first salt formula selected from the group consisting of KH2PO3, and K2HPO3, and at least a second salt selected from the group consisting of KH2PO4, K2HPO4, and K3PO4, in a mixture with an agriculturally acceptable carrier. The composition preferably comprises an aqueous solution wherein each salt is present in solution from about 20 millimolar to about 5% vol./vol. Alternatively, and more preferably, the actual volume by use will equal 21.7% by weight PO4 and 21.5% by weight PO3. Such composition can then be diluted to between 2% and 4% by volume. Importantly, the PO3 and PO4 must remain soluble, meaning not too much PO3 and PO4 can be added, otherwise the PO3 and PO4 will precipitate.
Phosphonate salts useful in the practice of the invention also include those organic and inorganic salts taught by U.S. Pat. Nos. 4,075,324 and 4,119,724 to Thizy et al., (see, e.g., col. 1, In. 51-69 through col. 2, In. 1-4).
The present invention relates to compositions and methods for use in preventing diseases, such as late blight, caused by the genus Phytophthora. In particular, the present invention relates to compositions and methods for use in preventing plant diseases caused by Phytophthora infestans. The composition is comprised of a phosphate (PO4) constituent and phosphonate (PO3) constituent, with it most preferred that a composition comprised of potassium phosphonate and potassium phosphate be used. Once the composition is formed, it can be applied to plants to prevent infection by Phytophthora infestans and manifestations related to the infection. The composition can be applied as either a dry mix or an aqueous solution to plants prior to infection by the Phytophthora infestans organism.
The composition for preventing Phytophthora infestans is prepared by combining phosphonate and phosphate constituents. Any of a variety of phosphates are suitable for use, including K2HPO4, K3PO4, KH2PO4, (NH3)2 HPO4, (NH3) H2PO4, and combinations thereof. The phosphonates, like the phosphates, can be selected from any of a variety of compositions, including K2HPO3, KH2PO3, (NH3)2 HPO3, (NH3) H2PO3, and combinations thereof. Any phosphate and phosphonate constituent combination can be used as long as infection by and manifestation of Phytophthora infestations is inhibited. Additionally, it is necessary for the constituents to have suitable solubility in a carrier and to be of a constitution to allow easy distribution in an area where plants to be treated are grown. More preferably, the phosphonate and phosphate constituents, when combined, will have a synergistic effect in inhibiting Phytophthora infestans. The most preferred phosphate PO4) and phosphonate PO3) constituents for use in preventing Phytophthora infestans infection are combinations of K2HPO3 and K2HPO4. As such, the phosphate (PO4) and phosphonate (PO3) constituents are combined to form the composition used to prevent Phytophthora infestans infection.
While the discussed constituents are preferred for use in treating plants and preventing infection by the Phytophthora organism, variations of the phosphate and phosphonate constituents can be used. As such, it is preferred if the compound comprises a fungicidally effective amount of at least a first salt having the following formula: 
and a second salt having the following formula: 
where R1 is selected from the group consisting of H, K, an alkyl radical containing form 1 to 4 carbon atoms, halogen-substituted alkyl or nitro-substituted alkyl radical, an alkenyl, halogen-substituted alkenyl, alkynl, halogen-substituted alkynl, alkoxy-substituted alkyl radical, ammonium substituted by alkyl and hydroxy alkyl radicals;
R2 and R3 are selected from a group consisting of H and K;
Me is selected from a group consisting of K, alkaline earth metal cations, aluminum atom, and the ammonium cation; and
n is a whole number from 1 to 3, equal to the valence of Me. 
The constituents should be preferably mixed with a suitable carrier to facilitate distribution to an area where the plants to be treated are grown. The carrier should be agriculturally acceptable, with water (H2O) most preferred.
As an example of how to form the composition, it is preferred to first form a potassium phosphonate aqueous solution, with the phosphonate formation as follows:
H3PO3 is produced by the hydrolysis of phosphorus trichloride according to the reaction: PCl3+3H2O greater than H3PO3+3HCl. The HCl is removed by stripping under reduced pressure, and the phosphonic acid (H3PO3) is sold as a 70% acid solution.
The phosphonic acid is then neutralized in aqueous solution by potassium hydroxide according to the reaction: H3PO3+KOH greater than KH2PO3+H2O to about pH 6.5, and to produce a 0-22-20 liquid weighing 11.15 lbs./ gal. This solution is commercially available and is sold under the trademark xe2x80x9cPhos-Mightxe2x80x9d by Foliar Nutrients, Inc., Cairo, Ga. 31728.
The phosphate (P4) is produced by reacting mono potassium phosphate (0-51.5-34) with 45% potassium hydroxide in aqueous solution to produce dipotassium phosphate, by the following reaction: KH2PO4+KOH greater than K2HPO4+H2O with a product density of 1.394 at 20xc2x0 C. and a solution pH of 7.6 producing a 0-18-20 analysis. This solution is commercially available and is sold under trademark xe2x80x9cK-Phosxe2x80x9d by Foliar Nutrients, Inc., Cairo, Ga. 31724.
After the potassium phosphonate and potassium phosphate constituents, or other phosphonate and phosphate constituents, are formed, they can be combined to produce the potassium phosphonate and potassium phosphate composition. This composition is used to then treat plants for the prevention of infection by the Phytophthora genus, especially Phytophthora infestans. 
Varying amounts of each compound, for example, K2HPO3, KH2PO3, K2HPO4, or KH2PO4 in an aqueous solution, are combined at rates ranging from 20 millimolar to 5% vol./vol., depending on crop host and the pathogen complex and level of infection. Alternatively, the amount of the first salt is equal to one part by weight and the amount of the second salt is equal to between 0.001 and 1,000 parts by weight. It is preferred if the composition is comprised of 21.7% K2HPO4 and 21.5% K2HPO3 or 11.8% PO4xe2x88x923 and 10.7% PO3xe2x88x922, all of which are soluble.
Once formed, the composition will be applied to various plants to prevent Phytophthora infestans infection. The preferable method of application is foliar, either by ground or aerial equipment, but is not limited to that method alone. Injection or soil applications, for example, could also be efficacious depending on specific crops and pathogens. While it is preferred to apply the composition in an aqueous solution, other forms of application may be used, including dusts, flowables, water dispersable granules, granules and inert emulsions, as well as oils. At least one application should be made; however, multiple applications of the composition can be made.
The inventive composition has utility on fruit crops, agronomic crops, ornamentals, trees, grasses, vegetables, grains, and floricultural crops, as well as some aquatic crops, including water cress. The crops most likely infected by Phytophthora infestans are potatoes (Solanum tuberosum) and tomatoes (Lycopersicon esculentum). As such, the present composition is especially useful in treating potato and tomato plants to prevent Phytophthora infection.
The following examples set forth the preferred concentrations and techniques for formulation thereof, as well as methods of application, use and test results demonstrating the efficacy of the inventive concentration in protecting plants against attack by Phytophthora infestans. It is to be understood, however, that these Examples are presented by way of illustration only, and nothing therein shall be taken as a limitation upon the overall scope of the invention. The specific components tested in the Examples were prepared and applied as follows.
In each of Examples 1 and 2, treatments were applied as a one gallon solution by a back pack sprayer, maintained at about 60 psi, in sufficient quantities of water to achieve thorough coverage. All treatments were applied to the appropriate number of experimental units assigned in a randomized complete block (CRB) design replicated four times.
As used in the examples, xe2x80x9cPercent Late Blightxe2x80x9d means the percent of plants that exhibit blight. xe2x80x9cLesions Per Plantxe2x80x9d relate to the number of lesions on a particular plant caused by the infectious inoculum. The xe2x80x9cNo. Infected Leafletsxe2x80x9d relates to the number of infected leaves per plant.